Eoseristalis alleni (Thompson, 1997):217

Eristalis alleni belongs to a group (Eristalis) characterized by wing venation (closed and petiolate cell R1 and sinuate vein R4+5), a basolateral setose patch on the hind femora, eye pilose, katepimeron bare, and wing bare apically. Eristalis alleni is similar in appearance to the males of Eristalis circe and E. persa, but is readily distinguished by its leg color.

The subgenus Eoeristalis differs from Eristalis sensu stricto by having katepimeron bare (pilose in Eristalis s.s.).

Eristalis alleni as an adult is a typical flower fly, visiting flowers for pollen and nectar. Males also hover in the air near flowering plants. Nothing specific is known of the immature stages, but they are probably similar to those of other eristaline flower flies. The maggots of eristaline flies live in aquatic habitats, breathing air through long tails which reach to the water surface (hence, are called rat-tailed maggots). They feed by filtering nutrients from the water.

This species is restricted to the higher elevations in Costa Rica and is found no where else. Hence, vulnerable to habitat destruction via human incursion and global warming.

Adapted from original description (Thompson 1997).

MALE.

Head: Black; face brownish orange except for black oral margin and a narrow medial black vitta which extends vertically above tubercle, brownish orange pilose, dull grayish white pollinose, with pollinosity thin, not obscuring ground color; gena grayish white pollinose; frontal and vertical triangle brownish orange pollinose, black pilose; eye brown pilose on dorsal 1/2, yellow on ventral 1/2; occiput silvery white pollinose, yellow pilose, with some black pile on dorsal 1/3; antenna orange except darker brown on dorsoapical 2/3 of basoflagellomere; arista orange, distinctly pilose, with pile about 1/2 as long as basoflagellomere width; eye contiguity short, about as long as ocellar triangle.

Thorax: Black, grayish brown pollinose; scutum with very indistinct pattern of darker pollinose narrow submedial and broader interrupted sublateral vittae, extensively black pilose, with orange pilose marginally (anteriorly, laterally and posteriorly); scutellum dark orange, dull, black pilose except apical margin yellow pilose; pleuron orange pilose except black pile dorsoposteriorly on anepisternum and posteriomedially on katepimeron; metasternum black pilose. Legs: Orange except black coxae, trochanters and basally on femora; orange pilose except black pilose on meso- and metacoxa, dorsoapical 1/3 of metafemur, dorsoposteriorly on metatibia; anterior spiracular fringe light brown; posterior spiracular fringe dark brown; halter brownish orange, black capitulum; plumula brown; calypter large, orange brown, with black margin and fringe; tegula black and orange pilose; basicosta black pilose; wing bare, light brown.

Abdomen: 1st sternum black, gray pollinose, yellow pilose; 2nd thru 4th sterna orange, rarely black medially, yellow pilose; 1st tergum black, gray pollinose, yellow pilose; 2nd tergum orange except black narrowly apicomedially, orange pilose except black on apical 1/3; 3rd tergum orange except small black basomedial macula, black pilose except orange on basal 1/4 and laterally; 4th tergum orange except for very small black basomedial macula, black pilose except for a few scattered intermixed orange pile basally and laterally; genitalia black, dull, yellow and black pilose.

FEMALE.

Similar, but darker; front orangish brown pollinose, black pilose, about 0.40 times as wide as head at antenna, tapering to about 0.20 times as wide dorsally; profemur sparsely black pilose posteriorly; meso- and metafemur extensively black pilose; sterna more extensively brownish black; terga more extensively black pilose, 2nd tergum black pilose on apicomedial 1/2, 3rd tergum entirely black pilose, 4th tergum extensively black pilose, only orange pilose laterally; 5th tergum orange basally, black on apical1/3, dull pollinose except shiny apically; 5th sternum black, shiny except pollinose apically and laterally.

Eristalis (Eoseristalis) alleni Thompson, 1997.

Thompson, F.C. (1997) Revision of the Eristalis flower flies (Diptera: Syrphidae) of the Americas south of the United States. Proceedings of the Entomological Society of Washington 99, 209-237. [1991.05.15]

Eristalis alleni has been collected on the flower of Seneico oerestedinaus Benth and on flowers of Roseaceae.

Eristalis alleni is known only from the central highlands of Costa Rica.